The present invention relates to energy storage devices, including lead-acid batteries, as well as electrodes and energy storage devices comprising such electrodes.
There is growing demand for batteries that enable high current to be drawn from the battery at various stages of operation, whilst being able to supply a lower, longer term current for other stages of operation. Such batteries are also required to be able to be recharged efficiently at high and low recharge rates. Applications for such batteries include use in conventional car battery applications, electric and hybrid electric vehicles, battery-powered vehicles such as forklift trucks, renewable energy applications such as solar panels and wind turbine where auxiliary battery power is required to smooth out power supply, and standby power applications such as UPS.
Whilst there have been many significant advances in the development of new batteries and power networks for vehicle and other applications, such batteries still suffer from a number of problems.
In all of these batteries, different demands are placed on the battery in terms of the current drawn from and recharged to the battery at various stages of operation. In the case of vehicle applications, as one example, a high rate of discharge is needed from the battery to enable acceleration or engine cranking in electric and hybrid electric vehicles, respectively. A high rate of recharging of the battery is associated with regenerative braking. In such high rate operations (and in high rate charging in other applications for the batteries) the battery preferably needs to be able to supply the high rate of discharge over a period of 1 minute or more.
In early stage lead-acid batteries used in these applications, failure of the battery tended to occur at the negative plate, as a result of progressive accumulation of lead sulphate on the surfaces of the negative plates. This occurs because the lead sulphate cannot be converted efficiently back to sponge lead during high rate recharging. Eventually, this layer of lead sulphate develops to such an extent that the effective surface area of the plate is reduced markedly, and the plate can no longer deliver the higher current demanded from the automobile. This significantly reduces the potential life span of the battery.
Recent improvements in the negative plates of such batteries has improved the situation to an extent that now the positive plates of the battery are likely to fail before the negative plates. It is therefore an object to improve the lifespan of the positive plates, and to further develop high performance batteries that make use of these improvements. There is also a need for modified batteries, such as lead-acid batteries, that generally have an improved life span and/or improved overall performance compared to current batteries.